Written and designed by Roy Shepherd. Special
thanks to my wonderful wife
Lucinda Shepherd, friend Robert Randell and various experts for their
support.

How Great Britain Formed

Britain’s
geological history and rock record is remarkably complex. When considered in
a broader context the rocks are actually telling the story of how Britain
has moved around the Earth’s surface and the various environments and events
it has encountered on the way. It can be described as a chronological list
of geological periods and their respective rock types: Carboniferous coals, Triassic
sandstones, Jurassic limestones and clays, Cretaceous
chalks, etc. The record is difficult to interpret because many processes
are acting at once: plate tectonics, continental drift, sea-level change and climate change.

Important concepts

Orogeny: when continental plates collide the
area of impact experiences uplift, typically producing
mountain-chains of deformed rock with associated volcanics. The
impact is referred to as an orogeny.

Rifting: continental plates can be pulled
apart, in a process known as rifting, and new oceanic crust is
generated between them. Prior to rifting the crust thins as it is
stretched, normally bringing the land surface below sea-level. When
rifting occurs molten material rises up, causing the crust to swell,
typically creating a mountainous ridge along the line of the rift (a
mid-ocean-ridge).

Supercontinents: the continental plates
repeatedly assemble to form a supercontinent which then rifts apart,
until the dispersed continents eventually reassemble again in a
different arrangement.

The two major divisions of the last eon are the Palaeozoic and
the Mesozoic, which are characterized by the assembly of the
supercontinent Pangea, and by its break-up respectively. Britain has
always been located on continental margins and, as such, has been
subject to collisions and rifting since the Precambrian.

It's sensible to pick up the story of Britain in the Cambrian as
Britain’s Precambrian history is complicated and poorly known.

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Cambrian - Ordovician – Silurian (550 - 400 million years ago)

Both England, Wales and Scotland are in the southern hemisphere but are
separated by the Iapetus Ocean. Scotland is attached to a plate
comprised mainly of North America and Greenland. England and Wales
are part of
an arc-shaped microcontinent, perhaps comparable to modern
Indonesia, along with Scandinavia and Newfoundland. England and
Wales, and
Scotland are both situated on continental margins and under marine
waters for most of this period.

The Iapetus Ocean is slowly closing and by the Silurian the two
continental blocks collide producing the Caledonian orogeny. The
Scottish Highlands and the Scandinavian Mountains are remnants of
this mountain chain. The collision brings England & Wales and Scotland together.

Devonian (400 - 350 mya)

The uplift of the Caledonian orogeny brings most of Britain
above sea-level and terrestrial sediments are shed off of the
Caledonian mountains. Britain is situated in the southern
desert-belt and the resulting sediments are arid sandstones (the Old
Red Sandstone).

The Caledonian Orogeny is largely over, but Britain is now
effected by a new orogeny to the south: the closure of the Rheic
Ocean which lies between Southern Europe and Northeast Africa. The
closure of the Rheic is one of the final stages of Pangea’s
assembly, as Africa and South America crash into North America and
Europe.

Carboniferous (350 - 280 mya)

Britain has now migrated into the equatorial forest-belt and
coal swamps abound. Sea-levels rise. The assembly of Pangea is
finally complete and Northeast Africa presses into Southern Europe
producing the Hercynian Orogeny. SW Britain lies within the
Hercynian mountain chain. Dartmoor, Bodmin Moor, and the other
igneous bodies of the SW are remnants of this collision event.

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Permian - Triassic (280 - 190 mya)

Britain enters the northern desert-belt. The assembly of Pangea
and the Hercynian Orogeny are accompanied by a worldwide drop in
sea-level. Britain is now in a very similar situation to the
Devonian: above sea-level, with mountains shedding sediment into a
desert environment (producing the New Red Sandstone).

Jurassic (190 - 140 mya)

Pangea begins to break-up and global
sea-levels begin to rise. Rifting begins in preparation for the
opening of the Atlantic Ocean. Britain is situated within the
immediate zone of rifting and begins to subside, allowing marine
waters to flood in from the Tethys (to the Southeast) and later from the
boreal too (to the North). Sea-levels fell again at the end of the
Jurassic.

Cretaceous (140 - 65 mya)

Global sea-levels rise again, and by the Late Cretaceous they
have reached what is possibly their all-time high. This probably
relates to the break-up of Pangea; intense and widespread rifting
activity causes the mid-ocean-ridges to swell, which in turn
displaces much of the ocean’s waters onto the continents. With much
of the land flooded there is little source for terrestrial
sediments, instead plankton deposit extensive chalks over much of
the continental shelves. The North Atlantic begins to open just west
of Britain.

Palaeogene (65 - 22 mya)

Atlantic opening spreads north between Britain and Greenland,
leading to volcanics along the west coast of Scotland and in
Northern Ireland. The islands of Aran, Mull and Skye are remnants of
these volcanoes, and the Antrim Basalts (including the Giant’s
Causeway) are remnants of the lava which flooded out. Africa,
Arabia and India are moving north towards Europe and Asia, closing the
Tethys Ocean.

Neogene (22 - 2 mya)

Tethys closes and glaciation begins. India and Arabia crash into
Asia, producing the Himalayan and Zagroa Mountains respectively.
Africa hits Europe creating the Alps, the effects of which reach
Britain creating the gentle but large scale folding seen in the
south (Isle of Wight, South Downs, North Downs, Weald). The
Mediterranean is a remnant of the Tethys which will eventually
close, and the volcanics in the region (Vesuvius, Etna, Stromboli,
etc.) are products of this closure.

Quaternary (2 - 0 mya)

Arctic ice-sheets periodically migrate south and then retreat as
global sea-levels simultaneously fall and rise.

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Left: A birthday party with
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Right: A family hold their prized ammonite at Beachy Head.

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References: Frames based on figures
in The Key to Earth History (1994), P. Doyle, M. R. Bennett and A. N.
Baxter. Global map provided by
www.scotese.com:
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Scotese, PALEOMAP Project, 700 Tanglewood Lane, Arlington, Texas 76012 Phone
(toll free) 888 288 0160, or 817 275 1697 Fax: 817 261 6293; email:
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